In a hydrostatic bearing the cooperating bearing surfaces are spaced apart by means of a layer of a pressure liquid, usually oil. The required oil pressure is generated by a pump system. Such a bearing has a large load carrying capacity and low friction. Low friction, however, depends on constantly maintaining a predetermined required oil pressure during operation. If the pressure for any reason should cease, e.g. at current interruption, the electric pump motors will stop and a metallic contact will result producing a high friction at the cooperating bearing surfaces which can easily lead to break-down, which, in turn, can result in large damages due to the usually large loads carried by the bearing. For security reasons, it is therefore necessary when current interruption occurs to ensure that the bearing is supplied with oil under sufficient pressure during a predetermined slow-down time period, that is, the time period which it takes to stop the member carried by the bearing.
It is for this purpose earlier known to accumulate a volume of oil under pressure, e.g. in a piston accumulator, which in principle consists of a cylinder wherein an axially freely moveable piston divides the cylinder volume in two parts, whereby oil in communication with the bearing pressure oil system is contained in one part of the cylinder and pressure gas in the other part thereof. The oil pressure and the gas pressure at each side of the freely moveable piston automatically will equalize themselves in order to balance the piston. As the gas is compressible, the gas volume thereby will vary in response to the oil pressure prevailing in the bearing, which bearing pressure in turn will vary in relation to the bearing load. The oil volume contained in the accumulator will hereby vary in response to the changes caused by the bearing load. The oil volume in the accumulator furthermore always must be sufficient for attending to the slow-down time. In bearings subjected to large load variations e.g. in mills, this means that the accumulator volume must be large and this volume is then only utilized to a very little part. The cost for the accumulator unit will therefore be considerable and it will amount to a large part of the entire cost of the bearing system. The required space is furthermore large. Other systems for preventing metallic contact between the bearing surfaces of hydrostatic bearings when pump failure occurs have been proposed. In accordance with these systems the pump system is connected to a fly wheel which will drive the pump during a predetermined time period after the current interruption. It has also been suggested to provide the supported member with auxiliary bearings, such as roller bearings, which operate or function when the pressure ceases in the hydrostatic bearing. Such solutions are however technically complicated, expensive and oftentimes of insufficient reliability